Chandra monitoring of UGC 4203: the structure of the X-ray absorber

TL;DR

This study uses Chandra observations to investigate rapid changes in X-ray absorption in UGC 4203, suggesting the torus and broad line region may be the same structure in AGN.

Contribution

It provides the first detailed monitoring of N_H variability in UGC 4203, linking the X-ray absorber to the broad line region in AGN.

Findings

X-ray absorbing column density varies on two-week timescales.

The X-ray torus may be the same as the broad emission line region.

This variability supports a unified structure in AGN circumnuclear media.

Abstract

We present a Chandra monitoring campaign of the highly variable Seyfert galaxy UGC 4203 (the "Phoenix Galaxy") which revealed variations in the X-ray absorbing column density on time scales of two weeks. This is the third, clear case, after NGC 1365 and NGC 7582, of dramatic N_H variability on short time scales observed in a "changing look" source, i.e. an AGN observed in the past in both a reflection-dominated and a Compton-thin state. The inferred limits on the distance of the X-ray absorber from the center suggest that the X-ray "torus" could be one and the same with the broad emission line region. This scenario, first proposed for an "ad-hoc" picture for NGC 1365, may be the common structure of the circumnuclear medium in AGN.